Self- assembly of Au@ Ag core- shell nanocubes embedded with an internal standard for reliable quantitative SERS measurements

摘要

Surface enhanced Raman spectroscopy (SERS) has emerged as a powerful spectroscopic tool, which offers information about the vibrational modes of molecules. However, performing quantitative analysis using SERS still faces great challenges. Here, we report a facile and reliable strategy for quantitative SERS determination using Au@Ag core-shell nanocubes (NCs) embedded with an internal standard (4-methylthiobenzoic acid) as the SERS substrate. To optimize the SERS property, Au@Ag NCs with finely tuned edge lengths in the range of 46 nm to 82 nm were synthesized. Au@Ag NCs with four different edge lengths were assembled into monolayer films using an interfacial self-assembly technique and transferred onto a silicon wafer. Their SERS performance was investigated using crystal violet (CV) as a target molecule and the corresponding electromagnetic (EM) near-field distribution was calculated using the FDTD method. The results clearly indicate that Au@Ag NCs with an edge length of 56 nm possess the highest Raman enhancement. Furthermore, we employed the Au@Ag NCs with an edge length of 56 nm, embedded with 4-methylthiobenzoic acid (4-MBA) as an internal reference, for quantitative SERS determination. Successful quantitative SERS measurements were demonstrated for CV in water and aspartame (APM) in drinks as analytes. The use of an internal standard and a monolayer film as a SERS substrate in solid form reduced the variability of the SERS signal and improved the reproducibility of the SERS response. To sum up, our approach is versatile and effective, and has the potential for the on-site quantitative detection of a wide variety of analytes.